This invention relates to brushless direct current (DC) three phase motors and, more particularly, to a start-to-run control circuit for driving the motor.
In an attempt to meet today's stringent automobile pollution standards as set by the government and further to increase fuel efficiency, the automobile industry is relying more and more on the use of fuel injected engines. To acceptably supply the fuel to the injectors of these fuel injection driven engines requires a fuel pump that pumps fuel in sufficient force to the injectors rather than the standard vacuum pump which draws fuel from the fuel tank to the injectors. At least one automobile manufacturer is including the fuel pump within the automobile fuel tank.
A brush-type DC motor with copper commutators is not suited for application within the fuel tank for the following reasons. The brush-type motor if placed in the fuel tank is subject to fuel contamination, generation of peroxides, high commutator wear rates and possible ignition of the combustible mixtures. Therefore, to overcome the disadvantages of the brush-type DC motor a brushless three phase DC motor is contemplated.
In order to properly operate the brushless DC motor it is necessary to have a control drive circuit to provide the necessary switching to the stator windings of the three phase stator so that a permanent magnet rotor, under the influence of the stator, will produce the speed/torque characteristics of a brush-type motor.
Thus, there is a need for a control circuit to produce both start and run modes of operation for operating the brushless three phase motor while providing variable starting frequency and speed dependent on the magnitude of the operating potential supplied to the circuit.